1. Field of the Invention
This invention relates to the field of wheels and, in particular, to caster wheels.
2. Description of the Prior Art
For many years, most high quality wheels for casters such as shopping carts have utilized bearings that include a pair of steel races and steel ball bearings, where each piece is assembled separately into the wheel. Because each part of this bearing assembly is assembled separately, the system relies on the precision of the interlocking structural parts to control the tightness of the bearing. Due to the inherent problems of mass-producing caster wheels with such precision, this method of production results in many caster wheels having less than the required tolerances to ensure a consistent smooth operation. This characteristic can frequently cause the well known xe2x80x9cwobble wheelxe2x80x9d. Additionally, the cost and inefficiency in manufacturing the assembly is high, and thereby translates to higher consumer pricing.
High strength polymer resin compounds have been used extensively for making wheels. More recently, the use of bearing components that molded in the hubs of such wheels has been suggested to absorb shock loads and to lower the cost of the wheel and bearing assemblies. But these assemblies are still complex to manufacture since the bearing parts must still be accurately placed within the mold. To ensure precision of the molded in bearing, the wheel hub must be precisely formed as well.
Representative of this method is U.S. Pat. No. 5,871,286 issued Feb. 16, 1999, which discloses a molded wheel having a bearing assembly molded into the wheel hub. The device includes a synthetic resin outer bearing race element embedded in the hub of the molded wheel and having a cylindrical inner sliding, journal type bearing surface. An inner bearing assembly includes two molded synthetic resin bearing halves having continuous cylindrical outer bearing surfaces disposed within the outer bearing race in sliding engagement with the inner bearing surface of the outer race. The bearing halves of the inner bearing assembly abut each other at their inner ends and may include interlocking structural features at their inner ends that enable securing of the bearing halves together at their inner ends while presenting a continuous outer cylindrical bearing sliding surface that cooperates with the adjacent surface of the outer race. A wheel axle extends through the inner bearing assembly and supports the wheel and bearing assembly for rotation relative to a wheel support.
Although the above invention overcomes some disadvantages of wheel bearings, there are still many disadvantages. First, the outer race is the only bearing element molded into the wheel hub. This leaves the bearing susceptible to the xe2x80x9cwobble wheelxe2x80x9d phenomenon due to uncontrollable looseness. This effect translates to bearing assemblies having inconsistent tolerances. Second, although this invention attempts to control potential looseness using an interlocking structure between the bearing halves, this means will suffer natural mechanical wear and tear resulting in the xe2x80x9cwobble wheelxe2x80x9d effect. Finally, although the process of making this invention lowers the cost of wheel and bearing assemblies, only the outer race is added to the wheel at the time of molding and the remainder of the bearing must be assembled at a later time, increasing the overall cost.
Therefore, there is a need for a molded wheel and bearing assembly and method of making the same, wherein the molded wheel can use a pre-assembled bearing assembly having high tolerances such that the tolerances of the molded wheel itself does not substantial adversely effect the overall performance of the finished wheel and, wherein the wheel can be incorporated into a caster support or other support well known in the art and, wherein the wheel can be produced faster and less expensively that wheels made using present manufacturing techniques.
Therefore, it is an aspect of the present invention to provide a molded wheel that can be produced less expensively than using present wheel construction methods.
It is another aspect of the invention to provide a molded wheel that is made using pre-assembled bearings having high tolerances.
Another aspect of the invention is to provide a molded wheel that uses butt out type bearing as the pre-assembled bearings.
Still another aspect of the invention is to provide a method of making a molded wheel using an easily fabricated housing to hold the pre-assembled bearings wherein the housing can be molded to high tolerances.
It is a further aspect of this invention to provide a simple method of molding a bearing assembly into a wheel suitable for use in a caster.
Another aspect of the invention is to provide a method of making a molded wheel that eliminates much of the assembly costs.
It is still another aspect of the invention to provide a method of making a molded wheel such that the hub of the wheel can be inexpensively molded yet the molded wheel will have high precision to ensure smooth operating of the wheel bearing assemblies.
Another aspect of the invention is to provide a method of making a molded wheel such that molding the hub can be accomplished with having substantially less scrap using prior art techniques.
It is still another aspect of the invention to provide a method of making a molded wheel where the need for much of the assembly equipment such as the machinery for making the bearing, assembly of the bearings into the hub, etc. can be eliminated.
Finally, it is an aspect of the invention to provide a method of making a molded wheel that can accomplished in a two step process and wherein the finished wheel is obtainable off the assembly line after the completion of the second step in the process.
The present invention provides a bearing assembly molded into a wheel. The bearing assembly includes two butt-out precision bearings, which are commercially available, and a molded housing, which can be easily manufactured. One bearing is positioned in each end of the housing. The complete bearing assembly is located in the center of the wheel surrounded by a molded hub. The molded tread is then placed on the molded hub to complete the wheel. The wheel can then be part of caster or other support structure.
The invention also provides a method of making a molded wheel and bearing assembly. A bearing assembly, including two butt-out bearings in a molded housing, is placed in the center of a wheel mold. The hub is molded around the assembly. A tread is then molded around the hub. A completed molded caster wheel can then be removed from the mold. Assembly of individual elements into the wheel is unnecessary.
These aspects of the invention are not meant to be exclusive. Other features, aspects, and advantages of the present invention will be readily apparent to those of ordinary skill in the art when read in conjunction with the following description, appended claims, and accompanying drawings.